Field of the Invention
The present invention relates to a torque estimating system for a synchronous electric motor.
Description of the Related Art
A permanent magnet synchronous electric motor is known in which permanent magnets are disposed in a rotor and the rotor is rotated by an interaction between the permanent magnets and a rotating magnetic field generated by a stator. As a method of detecting the torque of such an electric motor, Patent Literature 1 (Japanese Patent Application Publication No. Hei 10-28354) discloses a method of detecting the torque by using a torque sensor.
However, attaching the torque sensor to a rotating part of the electric motor as described in Patent Literature 1 may reduce the durability and reliability of the electric motor. Moreover, attaching the torque sensor increases the cost.
The present invention has been made in view of the problem described above and an object thereof is to provide a torque estimating system for a synchronous electric motor which can accurately estimate the torque of the electric motor in a wide operation range from zero speed to a high number of revolutions of the electric motor, without using a torque sensor.